An organic EL device is a light-emitting element utilizing electroluminescence of an organic compound. The organic EL device has an anode electrode and a cathode electrode and an electroluminescent organic emitting layer arranged between the electrodes. The organic compound contained in the electroluminescent organic emitting layer is broadly divided into a combination of low molecular weight organic compounds (a host material and a dopant material) and a high molecular organic compound. Examples of the electroluminescent high molecular organic compound include polyphenylene vinylene called PPV and derivatives thereof. It is said that the organic EL device utilizing a high molecular organic compound can be driven at a relatively low voltage, consumes less power and can easily comply with the increased size of the display panel, and therefore, R&D on the device is being conducted positively.
In the organic EL display panel using the organic EL device, an electroluminescent organic emitting layer is formed using printing technologies such as ink-jet method in each pixel depending on the color (R, G or B) of the light emitted.
A high molecular organic emitting layer is arranged in each pixel by applying a polymer ink containing, for example, an organic emitting material and a solvent by ink-jet method, and the like. In the case when an ink containing an organic emitting material is applied to each pixel, it is necessary to prevent the ink from overflowing to neighboring pixels.
For preventing the ink from overflowing to neighboring pixels, a method in which each pixel is defined by a dividing wall (a bank), and the ink is applied in a region defined by the bank is known (See for example, Patent Document 1).
In the case when the region defined by the bank is printed by the ink containing the organic emitting material, it is preferable that the wettability of the bank is low for preventing the ink from overflowing to the non-target area.
A fluorine component is generally known to decrease the surface energy of a material and decrease the wettability. For the reason, in order to form a bank having a top face of low wettability, a technology for subjecting the bank surface to plasma treatment using a fluorocarbon based gas is known (See, for example, Patent Document 2).
It is also proposed to form a bank using a fluorine containing resin (See, for example, Patent Document 3). A bank consisting of a fluorine containing resin formed by a photolithography process (coating; development; washing; baking) has a feature of low wettability without performing the plasma treatment.
In addition, in order to divide the functional layer of the organic EL device by pixel, a technology to form a groove or a protrusion on the top face of the bank is known. The functional layer divided by the groove or the protrusion formed on the top face of the bank is broadly divided into a layer formed by coating (for example, an organic emitting layer, Patent Documents 4, 5 and 6) and a cathode (Patent Documents 7, 8, 9, 10 and 11).
In the Patent Document 4, there is disclosed a technology to prevent the ink from overflowing to the neighboring pixels by concaving the top face of the bank even when the ink containing the material of the functional layer overflows from the region defined by the bank. According to the Patent Document 4, the concave of the top face of the bank is formed by heating and changing the shape of the bank.
In the Patent Document 5, there is described a technology to define the region where the ink containing the material of the functional layer is applied, by forming a bank consisting of an organic material on a bank consisting of an inorganic material. According to the Patent Document 5, the bank is subjected to the surface treatment in order to obtain the desired wettability.
In the Patent Document 6, there is disclosed a technology to prevent the ink from overflowing to the neighboring pixels by forming a groove on the top face of the bank consisting of a novolak resin even when the ink containing the material of the functional layer overflows from the region defined by the bank.
In addition, in the Patent Documents 7, 8, 9, 10 and 11, there are disclosed technologies for forming a groove or a protrusion on the top face of the bank to separate the cathode electrically.
Patent Document 1: U.S. Pat. No. 6,388,377
Patent Document 2: Japanese Patent Application Laid-Open No. 2005-52835
Patent Document 3: Japanese Patent Application Laid-Open (Translation of PCT Application) No. 2005-522000
Patent Document 4: Japanese Patent Application Laid-Open No. 2006-032198
Patent Document 5: U.S. Patent Application No. 2007/0252518
Patent Document 6: U.S. Patent Application No. 2005/0093441
Patent Document 7: Japanese Patent Application Laid-Open No. 2006-294454
Patent Document 8: Japanese Patent Application Laid-Open No. 2000-215989
Patent Document 9: Japanese Patent Application Laid-Open No. 2003-045668
Patent Document 10 U.S. Patent Application No. 2005/0285512
Patent Document 11: U.S. Patent Application No. 2005/0237780